During the development of muscle, proliferating myogenic cells differentiate and fuse to form multinucleate cells that synthesize proteins necessary for the assembly of striated myofibrils. One event previously shown by the applicant to be critical to this multistep process is the specific, Ca++-dependent adhesion of myoblasts prior to their fusion. The work proposed here aims to isolate and identify the cell surface molecules mediating myoblast recognition using a combined biochemical and immunological approach. Recent work by the applicant indicates that the cell surface adhesion molecules are glycoproteins. Adhesion glycoproteins are currently being purified from pectoral muscle explants and myoblast cultures using anion exchange and lectin affinity chromomatrophy. To date our active fraction contains eight glycoproteins. We are raising monoclonal and polyclonal, monospecific antibodies against these glycoproteins in an effort to isolate antibodies that inhibit Ca++-dependent myoblast adhesion. Monospecific, adhesion-perturbing antibodies will be used to identify and localize the adhesion glycoproteins and to study their expression during myogenesis.